Nobody should have to hack the binary of SMB. A lot of newer hackers have trouble understanding adding a mapper to a game that never had one.

I added some init routines, shuffled some routines around, and made SMB1 use the MMC1 mapper (easily reproduced, plenty powerful enough to do anything you want).

Using the new routines are explained in the readme file. I tried to keep it very simple, didn’t get complex the way some other games do it.

I’ve included a build script with the zip, which will likely need adapted to your own files, but should be easily understandable.